The invention concerns a method for the production of shaped and unshaped bodies with porous structure, such as fibers, foils, tubing, rods, shaped sections, powders, and the like, particularly though the production of membranes in the form of hollow filaments with adjustable total pore volume, adjustable pore size and adjustable pore walls.
Methods for the production of porous shaped bodies, whereby under "porous" not only a macroporous but also a microporous structure or mixed shapes of both are to be understood, have already been described in DE-OS 2 737 745. There, numerous polymers and liquids are given which can be worked up from a homogeneous solution according to determined methods into shaped bodies with interesting characteristics. Therewith for a determined polymer or a polymer combination, in each case a specific solvent is employed.
According to these methods, mainly shaped-body objects can be produced, with adjustable total pore volume. By altering the polymer portion in the solution, it is possible to vary the pore volume portion in the prepared shaped bodies within broad limits. Difficulties are caused, however, in simultaneously adjusting also the pore size to a desired value, since with increasing pore volume portion, also the size of the individual pores increases. It is indeed possible to control the pore size to a certain extent, by varying the cooling conditions; however, important limits are set, since at some times the cooling process can frequently be controlled very poorly, whereas at other times difficulties also occur upon deformation into shaped bodies, if one deviates in more or less great measure from determined cooling conditions. Thus, with very slow cooling, the shape cannot be retained, whereas too fast a cooling results in difficulties at the outlet of the implement used for the shaping, such as hollow filament nozzles, among others.
A further disadvantage of the method described in the reference is that a noticeable part of the there-recommended liquids is more or less toxic, so that the cost of extracting the toxic liquid after solidification of the shaped body is very high, particularly if the shaped body is supposed to be employed in medicinal fields, in the pharmaceuticals industry, in the foods industry, among others.
Similar problems as have been described above can also occur with the methods for the production of shaped bodies, as they are described for example in DE-OS 2 833 493 and in the German patent application P 30 26 718.6-41 of July 15, 1980.
Although numerous methods are already known which enable one to obtain bodies having porous structure, there exists however a need for improved methods, which lead to products with good and improved characteristics.